456 APPLIED SCIENCE 



539. Pewter. Pewter is a dull looking alloy formerly 

 used for making plates and dishes, beer measures, wine 

 measures, and large vessels. Good hard pewter is made of 

 tin, copper, and antimony, but a very inferior kind and that 

 most frequently met with at the present day, is made chiefly 

 of lead, a small proportion of tin, and copper. 



540. Common Solder and Fluxes. Solder is an alloy 

 used to stick metals together. It is a mixture of lead and 

 tin usually in the proportion of half and half. Many other 

 solders are used in soldering gold, silver, German silver, and 

 aluminum. Only pure metals can be soldered together. 



When the two metals are heated a scale, called an oxide, 

 forms on their surface. To prevent the formation of this 

 while soldering, a substance or liquid called a flux is applied 

 to the surfaces to be soldered. The flux acts by dissolving 

 the oxide formed and at the same time forms a coating which 

 prevents oxidation. 



There are a number of fluxes, such as rosin, zinc chloride, 

 muriatic acid, borax, and sal ammoniac, each of which has 

 a particular use. Rosin is used on sheet tin and seems to 

 act more effectively than zinc chloride, which is used on tin, 

 brass, copper, iron, and steel. Sal ammoniac is used in 

 tinning. 



541. Process of Soldering. Soldering or " sweating" is 

 a difficult operation. Careful investigations show that as 

 much as 90% of the soldering work done is defective. This 

 trouble is due principally to improper and careless cleaning 

 of the metal surfaces to be joined. Then again an improper 

 flux may be used. The most effective method- of soldering 

 is first to fit the parts accurately, to make the joint strong; 



